This invention relates to improvements in thawing of blood plasma units. Storing blood plasma in a frozen state and then thawing it when needed is a common practice in blood banks of hospitals and the like. For many years the typical practice in the blood bank has been to select the required unit of plasma and simply place it into a controlled temperature water bath to thaw the unit to the liquid state. After thawing, the plasma unit is removed from the water bath and is temperature controlled for use anytime during the next twenty-four hours.
Plasma units typically are in the form of a sealed, prepackaged plastic pouch, holding 250 milliliters of plasma. The pouch includes one or more connector tubes through which the plasma may flow when the unit is in use. The connector tubes typically are presealed with a plastic membrane which is punctured when the unit is connected to the delivery cathether, as by a needle set inserted into the tube to puncture the membrane.
The foregoing practice of simply placing the blood plasma unit into a water bath has, in some instances, resulted in bacterial contamination of the plasma unit. Bacteria in the water bath may contact the plastic pouch in which the plasma is contained. While the plastic pouch itself provides a barrier against direct contamination of the plasma within the pouch, water from the bath sometimes seeps into contact with the inlet end of the connector tube. Should bacteria develop in or near the connector tube, the possibility exists that when the connector tube seal is punctured by the needle set to evacuate the plasma, the plasma may be contacted by the bacteria thereby contaminating the plasma. This type of difficulty has resulted in recent suggestions to use techniques designed to avoid contamination of the plasma container, and particularly contamination of the entry ports. The suggested technique has been to place the plasma, frozen in its pouch, within a polyethylene or other plastic bag, preferably a bag in which the seal is an hermetic seal such as a heat sealed or a self-sealing bag. The pouch, thus overwrapped and completely protected, is placed in the water bath to thaw the plasma within the inner plasma pouch. While this technique appears to be effective in avoiding contamination during the thawing process, it does present some additional difficulties. Among the difficulties is that because the bag is overwrapped within a sealed outer bag the time required to thaw the plasma unit necessarily is increased. Additionally, the bag tends to float on the water which further increases the thawing time. Moreover, this technique requires special heat sealing equipment or expensive bags with self-sealing features. Typically, such self-sealing or heat sealable bags are of the order of a minimum of 2 to 3 mils thick which provides an additional thermal barrier which further increases the thawing time.
The present invention provides a technique and system which achieves thawing in a water bath, while maintaining the plasma bag in a dry, contaminant-free configuration, but in a manner which avoids foregoing difficulties. In accordance with the present invention, the frozen plasma unit is placed within a thin, open-topped plastic bag. The bag then is placed in a special holder associated with the water bath. The holder and the bag cooperate to maintain the plasma unit, which is within the lower end of the thin plastic bag, well submerged below the surface of the water. The thin, open topped plastic bag conforms closely to the shape and configuration of the frozen plasma container thereby avoiding any substantial insulative spaces which might retard the thawing process. The holder and water bath are specially constructed to facilitate easy attachment and detachment of the bag from the holder. After the thawing process has been completed, the plastic bag can be removed in its entirety and the still dry, thawed plasma unit may be removed with assurance that it has not been contaminated by bacteria as a result of contact with the thawing bath.
It is among the objects of the invention to provide an improved system for thawing frozen plasma units.
A further object of the invention is to provide an improved system for thawing frozen plasma samples which maintains the plasma sample in a dry condition while exposing it to the thawing heat from a fluid bath.
Another object of the invention is to provide a system of the type in which the thawing time is not materially increased.
A further object of the invention is to provide improved, yet simplified apparatus for practicing the invention.